Piezoelectric Bimorph Actuator Research Articles

Experimental Validation of One-Dimensional Model of an Ideal Bimorph Actuator Provided on Bidomain Lithium Niobate

The study demonstrates that the dynamic characteristics of piezoelectric bimorph actuators based on bidomain lithium niobate (BLN) single crystals are accurately described by an analytical one-dimensional (1D) model of an ideal bimorph. Our observations show that displacements and an electric impedance of the BLN-based bimorphs can be predicted without use of any sophisticated lumped circuit models, equations with handpicked “effective” values of material’s constants or finite element method. The experimental data were measured by means of laser interferometry and impedance spectroscopy and then fitted with the equations predicted by the 1D model. Solving the inverse problem for the experimental points we calculated the transverse piezoelectric coefficient, longitudinal mechanical compliance, dielectric permittivity, and piezoelectric coupling coefficient of the material. The obtained values of the material constants of the lithium niobate y + 128°-cut crystal are d23 = 25 pC/N, s33E = 7.58 TPa−1, ε22T = 52.7 ε0, and k232 = 0.18, which are in excellent agreement with the literature data.

Motion Characteristics of Self-Sensing Piezoelectric Actuator for Yarn Micro-Gripper

In order to solve the problem of low response frequency and poor consistency of conventional yarn grippers in weft accumulators, in this study, a piezoelectric yarn gripper is used instead of conventional yarn grippers and the motion characteristics of its actuator are studied. This gripper uses a bimorph piezoelectric bending actuator with a low-cost, well integrated self-sensing method based on charge measurement. The modeling of the piezoelectric micromanipulator is based on the piezoelectric and Euler–Bernoulli beam equations. The static and dynamic characteristics of the piezoelectric actuator as well as the self-sensing capability were experimentally tested. The experimental results show that the maximum output displacement at the end of the piezoelectric actuator is 834 μm, and the maximum output force is 388 μN at 150 V driving voltage. The stability and consistency of its response are also very good, with a response speed of 24 ms. The self-sensing test of the output force also proved the feasibility of the self-sensing method used, with an error of 0.74%. The piezoelectric yarn gripper studied in this paper is promising for practical clamping applications.

Computational evaluation of flight performance of flapping-wing nano air vehicles using hierarchical coupling of nonlinear dynamic and fluid-structure interaction analyses

This study endeavours to introduce an inventive hierarchical coupling methodology for evaluating the flight capabilities of polymer micromachined flapping-wing nano air vehicles (FWNAVs) using advanced computational tools. Furthermore, our objective is to provide a practical demonstration of FWNAVs in both tethered and airborne scenarios. These dual objectives represent the distinctive and pioneering aspects of this research. Such FWNAVs, which are insect-inspired robots, have a 2.5-dimensional structure. An FWNAV comprises a micro piezoelectric drive system and a pair of micro thin flexible wings. The drive system includes a micro transmission and a piezoelectric bimorph actuator. The flight performance of the designed FWNAV is evaluated using a hierarchical coupling approach, where the whole system is decomposed into a micro wing and a micro piezoelectric drive system. The coupling between these parts is modelled as one-way coupling and that between the micro wings and the surrounding air is modelled as strong coupling. In the one-way coupling analysis, nonlinear structural dynamic analysis is conducted for the micro piezoelectric drive system, where the dynamic response is transmitted to the micro wings via the Dirichlet boundary condition. In the strong coupling analysis, strongly coupled fluid-structure interaction analysis is conducted for the micro wings and the surrounding air to consider their strong coupling. The optimisation of flight performance is conducted using fluid-structure interaction analysis to achieve sufficient lift force to support the weight of an FWNAV. The design of a tethered and flyable FWNAV with a size of 10 mm or smaller is demonstrated. This FWNAV can be easily fabricated using polymer micromachining.

Design and Control of a Trapezoidal Piezoelectric Bimorph Actuator for Optical Fiber Alignment.

To align a pair of optical fibers, it is required that the micro actuators used be small and have the characteristics of high accuracy and fast response time. A trapezoidal piezoelectric bimorph actuator was proposed for pushing and pulling an optical fiber. Based on a mathematical model and finite element model established in this paper, we analyzed the output displacement and output force of the proposed trapezoidal piezoelectric actuator under the influence of structural parameters. Since the piezoelectric bimorph actuator had a hysteresis effect, we applied particle swarm optimization to establish a Prandtl-Ishlinskii (PI) model for actuator and parameter identification. Then, two control methods, namely feedforward control considering hysteresis effects and fuzzy proportional-integral-derivative (PID) control employing feedback, were proposed. Finally, a composite control model combining the two control methods with fewer tracking errors was designed. The results show that the output displacement of this actuator is larger than that of a rectangular one. Additionally, the fuzzy PID control has a lower response time (15 ms) and an overshoot (5%).

Piezoelectric Based Adaptive Wing for Flow Control

An attempt is made to develop a piezoelectric based adaptive wing concept that can be used in Micro Air Vehicle (MAV) and Unmanned Air Vehicle (UAV) applications. Laminar boundary layer separation is considered to be a significant problem in low Reynolds number vehicles like MAV. Recently, periodic excitation has gained much interest in the control of flow separation through energizing the boundary layer. In the present study, a piezoelectric bimorph actuator has been used to develop a mechanism that will deflect or vibrate a segment of the wing to produce the required thickness variation and achieve flow control. A Finite Element model of the adaptive wing is developed in ANSYS and numerical results are compared with experiments. A five percent increase in the camber has resulted in 4.39 percent additional lift at higher angles of attack.

Nonlinear adaptive tracking control of piezoelectric bimorph actuator using hybrid modeling approach

Piezoelectric bimorph actuator has the advantages of small size, fast response speed and high displacement accuracy, but its inherent hysteresis nonlinearity seriously affect the control accuracy and stability of the system. The dead-zone operator was incorporated into classical Prandtl–Ishlinskii model to enable the description of asymmetric hysteresis of piezoelectric bimorph actuator. A hybrid model approach was developed with neural network and improved Prandtl–Ishlinskii model, and it has the advantages of a neural network with ready-made training algorithms and improve the Prandtl–Ishlinskii (PI) model to describe the asymmetric hysteresis. The adaptive control method was derived from training algorithm of neural network, which can update the weight parameters of Play operator and Dead-zone operator in real time. Comparing the results without control, the RMSE of displacement error decreases by 61.35% with classic model, and decreases by 82.93% with hybrid model and proposed adaptive tracking control. Experimental results show that the proposed hybrid model and adaptive control approach can more effectively compensate the hysteresis of piezoelectric bimorph.

Smart hybrid active/semi-active distributed structural acoustic control of thin- and thick-walled piezo-sandwich bimorph spherical shell cloaks

A novel three dimensional underwater smart piezo-sandwich spherical shell cloak is designed and analyzed based on the hybrid active/semi-active distributed structural acoustic control strategy. The sandwich configuration consists of series- or parallel-connected piezoelectric (PZT) bimorph actuator skin layers collocated with a semi-active electro-rheological fluid (ERF) core layer. Two separate coupled elasto-acoustic formulations are systematically developed. The first model is based on the variational principle of structural mechanics and the approximate Kirchhoff-Love thin shell theory while the standard sliding mode control (SMC) scheme is utilized to activate the acoustic scattering extinction capability of the hybrid structure. The second model is built on the exact linear theory of 3D piezoelasticity and the classical state-space transfer matrix approach along with the active damping control (ADC) strategy. Extensive numerical simulations reveal that the best broadband backscattering cancellation performance can effectively be achieved with the smart hybrid active/semi-active bimorph piezo-sandwich spherical shell cloak operating in parallel connection. To quantify the overall cloaking performance of the proposed design, the percentage error (%Err) of the external cloaked field relative to the background incident pressure field is calculated at selected dominant structural resonance frequencies within eight designated frequency bands (regions I to VIII). The remarkable (near-perfect) cloaking performance of the parallel-connected thick-walled hybrid bimorph piezo-sandwich shell (25%shellcloak) is demonstrated in the intermediate to high frequency regions (i.e., below 1.5% error in regions I, and III to VIII). This excellent invisibility performance is somewhat degraded in a narrow low frequency band (i.e., up to 8% error in region II) which is primarily linked to the elasto-acoustic resonances due to the coherent coupling of various types of highly interacting fluid- and shell-borne peripheral waves. On the other hand, the superior cloaking performance of the parallel-connected thin-walled hybrid bimorph piezo-sandwich shell (7%shellcloak) is observed predominantly in the low frequency range (i.e., below 1.5% error in regions I and II), while this exceptional performance is gradually degraded as the incident wave frequency is increased (i.e., up to 6.5% error in regions III to VIII), where partial or directional cancellation of the scattered field mostly occurs. Also, some important practical issues and limitations regarding the experimental implementation of proposed hybrid active/semi-active acoustic cloaking device are briefly discussed.

Importance of Three-Dimensional Piezoelectric Coupling Modeling in Quantitative Analysis of Piezoelectric Actuators

This paper demonstrates the importance of three-dimensional (3-D) piezoelectric coupling in the electromechanical behavior of piezoelectric devices using three-dimensional finite element analyses based on weak and strong coupling models for a thin cantilevered piezoelectric bimorph actuator. It is found that there is a significant difference between the strong and weak coupling solutions given by coupling direct and inverse piezoelectric effects (i.e., piezoelectric coupling effect). In addition, there is significant longitudinal bending caused by the constraint of the inverse piezoelectric effect in the width direction at the fixed end (i.e., 3-D effect). Hence, modeling of these effects or 3-D piezoelectric coupling modeling is an electromechanical basis for the piezoelectric devices, which contributes to the accurate prediction of their behavior.

Robust Control of a Bimorph Piezoelectric Robotic Manipulator Considering Ellipsoidal-Type State Restrictions

The current study presents an adaptive control approach to solve the tracking trajectory problem for a robotic manipulator that uses a gripper based on bimorph piezoelectric actuators. The development of an adaptive gain state feedback form that considers the state restrictions is proposed using a novel class of barrier Lyapunov function that drives the effective control of joints and piezoelectric actuators. The proposed method allows for the inclusion of complex combinations of state restrictions in the Lyapunov function, yielding the construction of differential forms for the gains in the controller that can handle the evolution of trajectories of the robotic arm inside the restricted region. The proposed control design successfully tracks reference trajectories for both joints of the robotic arm as well as the motion of the piezoelectric device during several operative scenarios. A comprehensive experimental study evaluates the effect of introducing state-dependent gain considering state restrictions of the ellipsoidal type. The comparison of the mean square error confirms the contributions of the developed control action, showing better tracking quality for less control power with the same evaluation, which is a desirable characteristic in the controlled motion of micromanipulators. The proposed controller solves the tracking trajectory problem for the micromanipulation system, satisfies the motion restrictions, and allows better tracking performance to be enforced. Furthermore, comparison of the obtained trajectories seems to validate the proposed controller’s contribution concerning a feedback form with fixed gains.

A 3-DOF inertial impact locomotion robot constructed on four piezoelectric bimorph actuators

An inertial impact locomotion robot (IILR), consisting of a base, three supporting feet and four vertically distributed piezoelectric bimorph actuators (PBAs), was developed in this work. The IILR could complete plane locomotion with three degrees of freedom (DOFs), including translation along X-axis, translation along Y-axis and rotation around Z-axis. The inertial impact force driving the IILR was generated by the PBAs through vibration. A simplified dynamic model of the IILR was established to predict its locomotion characteristics. Then, a prototype was fabricated, whose size was Φ114 × 14 mm3 and weight was 160.5 g. Then the locomotion performances and carrying capability of the IILR were tested, the results indicated that the maximum linear velocity was 76.66 μm s−1 and the maximum rotary velocity was 161.19 μrad s−1 under voltage of 600 Vp-p and frequency of 9 Hz, respectively. In addition, the maximum carrying load was 1600 g (about 9.97 times of self-weight). The experiment results were also in good agreement with the dynamics simulation results. Overall, the IILR held the characteristics of multiple DOFs, large carrying capability, simple structure and no electromagnetic interference; therefore, it could be suitable for precision positioning and carrying applications such as wafer inspection, microscopic observation and operation.

Computational control for strongly coupled structure, electric, and fluid systems

Piezoelectric-structure interaction (PSI) and fluid-structure interaction (FSI) are multi-physics coupled systems. These interactions affect the vibration characteristics of coupled systems and thus such complex coupled systems must be controlled. This paper proposes computational control based on the finite element method for strongly coupled multi-physics analysis of the PSI of a thin flexible piezoelectric bimorph actuator. The vibration characteristics and the effect of direct velocity and displacement feedback (DVDFB) control in coupled systems are investigated. The displacement and velocity feedback gains are used together as well as separately. DVDFB control is extended to the FSI of stiff and soft structures to study vibration characteristics using active control and compare the stability of the two types of structure. The results of PSI show a reduction in actuator displacement amplitude and a shift in the resonance frequency due to DVDFB control. For FSI, the results for a stiff material show a reduction in displacement. The velocity feedback gain has no effect for a stiff material and leads to instability due to a large control force. The results for a soft material show a reduction in displacement and amplitude and more stability compared to the case for the stiff material.

Cantilevered adaptive fiber-optics collimator based on piezoelectric bimorph actuators.

A novel, to the best of our knowledge, cantilever construction design of an adaptive fiber-optics collimator (AFOC) based on piezoelectric bimorph actuators for tip/tilt control is introduced. With this new cantilever structure, an AFOC with a diameter of only 6 mm was developed, and the output laser beam deviation angle and resonance frequency of the device were measured. The experimental results show that this new AFOC can provide more than 1 mrad deflection angle at a 20 V driving voltage, and the first resonance frequency is about 500 Hz. Further, in order to verify whether the cantilever structure can be used in a high-power fiber collimator, a high-power X-Y positioner with an 8 mm diameter fiber end cap was developed. The experimental results show that the high-power X-Y positioner can output more than 2 kW laser power and provide about 330 µm displacement of the fiber end cap in the X direction and about 770 µm in the Y direction at a 150 V driving voltage.

Nonlinear ESO-based vibration control for an all-clamped piezoelectric plate with disturbances and time delay: Design and hardware implementation

Considering the problems of model uncertainties, higher harmonics, uncertain boundary conditions, external excitations, and system time delay in practical vibration control system, a novel active vibration control method is proposed to suppress the vibration of a thin plate structure with acceleration sensor and piezoelectric bimorph actuator in this paper. First, a nonlinear extended state observer (NESO)-based controller is designed to ensure the anti-disturbance performance of the structural vibration control system. Then, an enhanced differentiator-based time delay compensation method is introduced to improve the vibration suppression performance of the NESO-based controller. A real time hardware-in-the-loop benchmark for an all-clamped piezoelectric thin plate is designed to verify and compare the performance of the developed controller against conventional ESO-based methods (linear ESO with/without time delay compensation, NESO without time compensation). The best vibration suppression and disturbance rejection performance of the proposed NESO-based controller with an enhanced time delay compensator is verified in the comparative experimental results. This work is able to provide practitioners with vital guidance in designing active vibration control system in the presence of disturbances and time delay.

Electric field-induced nonlinear behavior of lead zirconate titanate piezoceramic actuators in bending mode

In this article, analytical solutions of piezoelectric bimorph and unimorph actuator in cantilever configurations are developed using the second-order constitutive equation. Tip deflection ratio (TDR), a dimensionless parameter, is defined to analyze the effect of second-order coefficients of piezoelectric materials on the response of bimorph and unimorph actuators. Four piezoelectric unimorphs of varying geometries are fabricated and tested to verify the nonlinear response under applied electric field. Furthermore, second-order coefficients of lead zirconate titanate (PZT; APC 850) are derived by fitting the experimental data with nonlinear analytical solution. The nonlinear response of all the piezoelectric unimorphs compares well with the experimental results.

A streamlined fabrication process for high energy density piezoelectric bending actuators

Fabrication of high-performance actuators is often a bottle-neck in the creation of microrobots. In this work, we present a new approach to piezoelectric bimorph actuator fabrication that simplifies the process (in part by reducing the number of materials used) without sacrificing actuator performance. We fabricate PZT bimorph actuators with two active layers, as well as bimorphs with four active layers that are under 2 mm wide – these are more challenging to fabricate than the two-layer bimorphs and thus present a useful test case for our new process. The blocked force and free deflection of the actuators agrees well with expected performance, with energy densities of approximately 1.2 J/kg at electric fields of 1.67 V/µm. We expect this process to enable rapid fabrication of piezoelectric actuators with more layers and at smaller scales than was previously attainable.

Design, Modeling, and Analysis of Piezoelectric-Actuated Device for Blood Sampling

In recent years, micro electro-mechanical system (MEMS)-based biomedical devices have been investigated by various researchers for biomedicine, disease diagnosis, and liquid drug delivery. The micropump based devices are of considerable significance for accurate drug delivery and disease diagnosis. In the present study, design aspects of the piezoelectric actuated micropump used for extraction of blood sample are presented. A pentagonal microneedle, which is an integral part of the micropump, was used to extract the blood volume. The blood was then delivered to the biosensor, located in the pump chamber, for diagnosis. The purpose of such low-powered devices is to get sufficient blood volume for the diagnostic purpose at the biosensor located within the pump chamber, with a minimum time of actuation, which will eventually cause less pain. ANSYS® simulations were performed on four quarter piezoelectric bimorph actuator (FQPB) at 2.5 volts. The modal and harmonic analysis were carried out with various load conditions for FQPB. The extended microneedle lengths inside the pump chamber showed improved flow characteristics. Enhanced volume flow rate of 1.256 µL/s was obtained at 22,000 Hz applied frequency at the biosensor location.

Opto-mechanical modeling and experimental implementation of an FBG-based piezoelectric bimorph actuator for high voltage sensing applications

This paper proposes a highly simplified optical voltage sensor by using a piezoelectric bimorph and a Fiber Bragg Grating (FBG) that can be used for high voltage applications with a relatively good accuracy and stability. In this work the theoretical framework for the whole opto-mechanical operation of the optical sensor is detailed and compared to experimental results. In the analysis, a correction term to the electric field is derived to account for the linear strain distribution across the piezoelectric layer improving the designing equations and giving more criteria for future developments. Finally, some experimental results from a laboratory scale optical-based high voltage sensing setup are discussed, and shown to be in excellent agreement with theoretical expected behavior for different voltage magnitudes.

Study on a new type of miniature piezo walking robot

The development of a small-scale piezoelectric-driven walking robot is presented in this paper. Eight pieces of piezoelectric bimorph actuators are employed in the proposed design to achieve a direct drive. The displacement amplification mechanism of the robot is not required to minimize the weight and complexity. This robot is composed of four inner legs and four outer legs with a slop to the ground. Two square wave signals with a phase difference of 180° are used to realize bidirectional motion. First, the constitutive equation of piezoelectric bimorph with elastic support layer under external voltage and force is deduced. Then, the robot gait cycle is described, and the velocity expression of the robot is established using the kinematic analysis to predict the robot’s motion. Afterward, a prototype is fabricated on the basis of the proposed design. Finally, an experimental test is conducted for characterizing the walking robot. The design methodology can be applied to the development of the other piezoelectric robot for bidirectional motion.

Polypyrrole and poly(3,4-ethylenedioxythiophene) on silicon cantilever: Role of formation potential in bending displacement

The feasibility of conducting polymer bending actuators deposited on free-standing conductive silicon cantilevers was studied in this work. The motivation is the micro-system-technique, where mostly silicon bimorph piezoelectric actuators have been applied. Polypyrrole (PPy) and poly(3,4-ethylenedioxythiophene) (PEDOT) with various formation potentials were studied. The formation potential 1.1 V was found optimal for both materials, while PEDOT outperformed PPy in virtually every aspect. Long-term durability tests of 1000 cycles showed that activity was maintained, with PEDOT holding up better than PPy. The results show that conducting polymers, especially PEDOT, could be viable active materials for Si-based bilayer actuators, with low driving voltages to reach significant displacements.

A driving power with filter compensator for micro-positioning improvement of piezoelectric bimorph actuators

To improve the micro-positioning accuracy of piezoelectric bimorph actuators, a driving power was designed with filter compensator. Amplifier modular was designed with high-voltage operational amplifier, and filter compensator modular is responsible for charge signal. Simulation results show that the output of filter compensator modular is proportional to the electric charge on the actuator. Experimental results indicate that the maximum error is 10μm without filter compensator modular, and reduced to 5μm with proposed driving power.